Coated substrate created by systems and methods for modulation of power and power related functions of PECVD discharge sources to achieve new film properties

ABSTRACT

A method of generating a film during a chemical vapor deposition process is disclosed. One embodiment includes creating a substrate by generating a first electrical pulse having a first pulse amplitude; using the first electrical pulse to generate a first density of radicalized species; disassociating a feedstock gas using the radicalized species in the first density of radicalized species, thereby creating a first deposition material; depositing the first deposition material on a substrate; generating a second electrical pulse having a second pulse amplitude, wherein the second pulse amplitude is different from the first pulse width; using the second electrical pulse to generate a second density of radicalized species; disassociating a feedstock gas using the radicalized species in the second density of radicalized species, thereby creating a second deposition material; and depositing the second plurality of deposition materials on the first deposition material.

PRIORITY

The present invention claims priority to commonly owned and assignedpatent application Ser. No. 11/264,596 entitled SYSTEM AND METHOD FORMODULATION OF POWER AND POWER RELATED FUNCTIONS OF PECVD DISCHARGESOURCES TO ACHIEVE NEW FILM PROPERTIES, which is incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to power supplies, systems, and methodsfor chemical vapor deposition.

BACKGROUND OF THE INVENTION

Chemical vapor deposition (CVD) is a process whereby a film is depositedon a substrate by reacting chemicals together in the gaseous or vaporphase to form a film. The gases or vapors utilized for CVD are gases orcompounds that contain the element to be deposited and that may beinduced to react with a substrate or other gas(es) to deposit a film.The CVD reaction may be thermally activated, plasma induced, plasmaenhanced or activated by light in photon induced systems.

CVD is used extensively in the semiconductor industry to build upwafers. CVD can also be used for coating larger substrates such as glassand polycarbonate sheets. Plasma enhanced CVD (PECVD), for example, isone of the more promising technologies for creating large photovoltaicsheets, LCD screens, and polycarbonate windows for automobiles.

FIG. 1 illustrates a cut away of a typical PECVD system 100 forlarge-scale deposition processes—currently up to 2.5 meters wide. Thissystem includes a vacuum chamber 105 of which only two walls areillustrated. The vacuum chamber 105 houses a linear discharge tube 110.The linear discharge tube 110 is formed of an inner conductor 115 thatis configured to carry a microwave signal, or other signals, into thevacuum chamber 105. This microwave power radiates outward from thelinear discharge antenna 115 and ignites the surrounding support gas 120that is introduced through the support gas tube 120. This ignited gas isa plasma and is generally adjacent to the linear discharge tube 110.Radicals generated by the plasma and electromagnetic radiationdisassociate the feedstock gas(es) 130 introduced through the feedstockgas tube 125 thereby breaking up the feedstock gas to form newmolecules. Certain molecules formed during the dissociation process aredeposited on the substrate 135. The other molecules formed by thedissociation process are waste and are removed through an exhaust port(not shown)—although these molecules tend to occasionally depositthemselves on the substrate. This dissociation process is extremelysensitive to the amount of power used to generate the plasma.

To coat large substrate surface areas rapidly, a substrate carrier (notshown) moves the substrate 135 through the vacuum chamber 105 at asteady rate, although the substrate 135 could be statically coated insome embodiments. As the substrate 135 moves through the vacuum chamber105, the dissociation should continue at a steady rate and targetmolecules from the disassociated feed gas theoretically deposit on thesubstrate, thereby forming a uniform film on the substrate. But due to avariety of real-world factors, the films formed by this process are notalways uniform.

Nonconductive and conductive films deposited utilizing plasma enhancedchemical vapor sources have been achieved with many types of powersources and system configurations. Most of these sources utilizemicrowaves, radio frequency (RF), high frequency (HF), or very highfrequency (VHF) energy to generate the excited plasma species.

Those of skill in the art know that for a given process condition andsystem configuration of PECVD, it is the average power introduced intothe plasma discharge that is a major contributing factor to the densityof radicalized plasma species produced. These radicalized plasma speciesare responsible for disassociating the feedstock gas. For typical PECVDprocesses, the necessary density of produced radicalized species fromthe plasma must be greater than that required to fully convert allorganic materials. Factors such as consumption in the film depositionprocesses, plasma decomposition processes of the precursor materials,recombination losses, and pumping losses should be taken intoconsideration.

Depending upon the power type, configuration and materials utilized, therequired power level for producing the necessary density of radicalizedplasma species can unduly heat the substrate beyond its physical limits,and possibly render the films and substrate unusable. This primarilyoccurs in polymer material substrates due to the low melting point ofthe material.

To reduce the amount of heat loading of the substrate, a method of highpower pulsing into the plasma, with off times in between the pulsing,can be used. This method allows the plasma during the short high energypulses to reach saturation of the

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention that are shown in thedrawings are summarized below. These and other embodiments are morefully described in the Detailed Description section. It is to beunderstood, however, that there is no intention to limit the inventionto the forms described in this Summary of the Invention or in theDetailed Description. One skilled in the art can recognize that thereare numerous modifications, equivalents and alternative constructionsthat fall within the spirit and scope of the invention as expressed inthe claims.

One embodiment includes creating a coated substrate by generating afirst electrical pulse having a first pulse amplitude; using the firstelectrical pulse to generate a first density of radicalized species;disassociating a feedstock gas using the radicalized species in thefirst density of radicalized species, thereby creating a firstdeposition material; depositing the first deposition material on asubstrate; generating a second electrical pulse having a second pulseamplitude, wherein the second pulse amplitude is different from thefirst pulse width; using the second electrical pulse to generate asecond density of radicalized species; disassociating a feedstock gasusing the radicalized species in the second density of radicalizedspecies, thereby creating a second deposition material; and depositingthe second plurality of deposition materials on the first depositionmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects and advantages and a more complete understanding of thepresent invention are apparent and more readily appreciated by referenceto the following radicalized species required for the film depositionprocess and loss to occur, while reducing the instantaneous andcontinuous heating of the substrate through the reduction of other formsof electromagnetic radiation.

Film property requirements are achieved by setting the processconditions for deposition, including the power levels, pulsing frequencyand duty cycle of the source. To achieve required film properties thestructure and structural content of the deposited film must becontrolled. The film properties can be controlled by varying the radicalspecies content, (among other important process parameters), and asstated in the above, the radical density is controlled primarily by theaverage and peak power levels into the plasma discharge.

To achieve several important film properties, and promote adhesion tosome types of substrates, the films organic content must be finelycontrolled, or possibly the contents must be in the form of a gradientacross the entire film thickness. Current technology, which enablescontrol of only certain process parameters, cannot achieve this finecontrol. For example, current technology consists of changing thedeposition conditions, usually manually or by multiple sources andchambers with differing process conditions, creating steps in the filmstack up to achieve a gradient type stack. Primarily the precursor vaporcontent, system pressure, and or power level at one or more times isused to develop a stack of layers. These methods are crude at best anddo not enable fine control. Accordingly, a new system and method areneeded to address this and other problems with the existing technology.

Detailed Description and to the appended claims when taken inconjunction with the accompanying Drawing wherein:

FIG. 1 illustrates one type of PECVD system;

FIG. 2 a illustrates a power supply for a PECVD system in accordancewith one embodiment of the present invention;

FIG. 2 b is an alternative depiction of a power supply for a PECVDsystem in accordance with one embodiment of the present invention;

FIG. 3 illustrates one example of a pulse-width modulated power signal;

FIG. 4 illustrates one example of a pulse-amplitude modulated powersignal;

FIG. 5 illustrates one example of a frequency-modulated power signal;

FIG. 6 a illustrates one example of a gradient film formed usingpulse-width modulation;

FIG. 6 b illustrates one example of a multi-layer gradient film formedusing pulse-width modulation;

FIG. 7 a illustrates one example of a gradient film formed usingamplitude-width modulation;

FIG. 7 b illustrates one example of a multi-layer gradient film formedusing amplitude-width modulation; and

FIGS. 8 a-8 d illustrate the development of a multi-layer gradient filmover time using a pulse-width modulated power signal.

DETAILED DESCRIPTION

In some PECVD processes the typical radical lifetime (time for the lossof and consumption of the radical species) is long enough so that therecan be an off time of the plasma during which the radical densityremaining is gradually consumed by the deposition of the film and lossmechanisms. Therefore, by controlling the total radical density duringthese on and off times of the plasma the chemical makeup of the film canbe altered, as well as the over all layer properties of the film.

By modulating the power level into the plasma, the on time of the plasmaand the timing between the power pulses, the user can make films thatwere not achievable before in PECVD. The layers could be a singlegradient layer or a multiple stack of hundreds to thousands of microlayers with varying properties between each layer. Both processes cancreate a unique film.

FIG. 2 a illustrates a system constructed in accordance with oneembodiment of the present invention. This system includes a DC source140 that is controllable by the pulse control 145. The terms “DC source”and “DC power supply” refer to any type of power supply, including thosethat use a linear amplifier, a non-linear amplifier, or no amplifier.The DC source 145 powers the magnetron 150, which generates themicrowaves, or other energy waves, that drive the inner conductor withinthe linear discharge tube (not shown). The pulse control 145 can contourthe shape of the DC pulses and adjust the set points for pulseproperties such as duty cycle, frequency, and amplitude. The process ofcontouring the shape of the DC pulses is described in the commonly ownedand assigned attorney docket number APPL-008/00US, entitled “SYSTEM ANDMETHOD FOR POWER FUNCTION RAMPING OF MICROWAVE LINEAR DISCHARGESOURCES,” which is incorporated herein by reference.

The pulse control 145 is also configured to modulate the DC pulses, orother energy signal, driving the magnetron 150 during the operation ofthe PECVD device. In some embodiments, the pulse control 145 can beconfigured to only modulate the signal driving the magnetron 150. Ineither embodiment, however, by modulating the DC pulses, the power levelinto the plasma can also be modulated, thereby enabling the user tocontrol radical density and make films that were not achievable beforein PECVD. This system can be used to form variable, single gradientlayers or a multiple stack of hundreds to thousands of micro layers withvarying properties between each other.

FIG. 2 b illustrates an alternate embodiment of a power supply. Thisembodiment includes an arbitrary waveform generator 141, an amplifier142, a pulse control 145, a magnetron 150, and a plasma source antenna152. In operation, the arbitrary waveform generator 141 generates awaveform and corresponding voltage that can be in virtually any form.Next, the amplifier 142 amplifies the voltage from the arbitrarywaveform generator to a usable amount. In the case of a microwavegenerator (e.g., the magnetron 150) the signal could be amplified from+/_(—)5VDC to 5,000 VDC. Next, the high voltage signature is applied tothe magnetron 150, which is a high frequency generator. The magnetron150 generates a power output carrier (at 2.45 GHZ in this case) that hasits amplitude and or frequency varied based upon the originallygenerated voltage signature. Finally, the output from the magnetron isapplied to the source 152 to generate a power modulated plasma.

Signal modulation can be applied by the pulse control 145 to thearbitrary waveform generator 141. Signal modulation is a well-knownprocess in many fields—the most well known being FM (frequencymodulated) and AM (amplitude modulated) radio. But modulation has notbeen used before to control film properties and create layers duringPECVD. Many forms of modulation exist that could be applied to awaveform power level, duty cycle or frequency, but only a few aredescribed below. Those of skill in the art will recognize other methods.Note that modulation is different from simply increasing or decreasingthe power or duty cycle of a power signal into a source.

FIG. 3 illustrates pulse-width modulation, which varies the width ofpulse widths over time. With pulse-width modulation, the value of asample of data is represented by the length of a pulse.

FIG. 4 illustrates pulse-amplitude modulation, which is a form of signalmodulation in which the message information is encoded in the amplitudeof a series of signal pulses. In the case of plasma sources the voltage,current or power level can be amplitude modulated by whatever percentagedesired.

FIG. 5 illustrates frequency modulation (FM), which is the encoding ofinformation in either analog or digital form into a carrier wave byvariation of its instantaneous frequency in accordance with an inputsignal.

Referring now to FIGS. 6 and 7, they show two examples of multi-layerfilms that could be produced with two differing forms of modulation,pulse-width and pulse-amplitude modulation. Both of these figuresillustrate the film layers deposited on the substrate and thecorresponding modulated power signal that is used to generate theplasma. Notice that the power signal is modulated during the depositionprocess, which differs from establishing and leaving initial set pointsthat are static during the deposition process.

Referring first to FIG. 6 a, it illustrates a variable film 157 producedby pulse-width modulation. In this embodiment, the cycle between shortpulse widths and long pulse widths is relatively long. This long cycleproduces a variable-gradient coating on the substrate that variesthrough its thickness from a flexible, organo-silicon film located nextto the substrate to a rigid, dense SiO2 or SiOxNy film. The filmproduced by this process becomes harder and more rigid as it extends outfrom the substrate.

A benefit is realized with this single, variable gradient layer becausethe flexible, softer portion of the film bonds better to the substratethan would the dense, rigid portion. Thus, the pulse width modulationallows a film to be created that bonds well with the substrate but alsohas a hardened outer portion that resists scratches and that has goodbarrier properties. This type of film could not be efficiently createdwithout a modulated power signal.

By changing the modulation of the power signal, a multilayer gradientcoating can be deposited on the substrate. FIG. 6 b illustrates thistype of substrate and film 160. In this embodiment, the cycle betweenshort pulse widths and long pulse widths is relatively short, therebycreating multiple layers. These individual layers can also vary fromless dense to more dense within a single layer—much as the singlegradient layer in FIG. 6 a does.

In this embodiment, a less-dense, organo-silicon layer is initiallydeposited on the substrate. This type of layer bonds best with thesubstrate. The next layer is slightly more dense, and the third layer isan almost pure SiO2 or SiOxNy layer, which is extremely dense and hard.As the pulse width modulates to shorter pulse widths, the next layer isagain a less-dense, organo-silicon layer that bonds easily to the denselayer just below. This cycle can repeat hundreds or even thousands oftimes to create a multilayer, gradient film that is extremely hard,resilient, and with good barrier properties. Further, this film can beproduced with a minimal amount of heat and damage to the substrate.

FIGS. 7 a and 7 b illustrate another series of films similar to thoseshown in FIGS. 6 a and 6 b. These films, however, are created usingpulse-amplitude modulation. Again, both a single gradient film 165 or amultilayer gradient film 170 can be created using modulation techniques.Note that this process works for almost any precursor and is not limitedto silicon-based compounds.

Variable films can be created with other modulation techniques. In fact,there are many modulation technologies that could be implemented toeffectively control the radical species density and electromagneticradiation in relation to time, including, PWM—Pulse Width Modulation,PAM—Pulse Amplitude Modulation, PPM—Pulse Position Modulation,AM—Amplitude modulation, FM—Frequency Modulation, etc. Again, thesetechniques involve modulating a power signal during film depositionrather than setting an initial power point or duty cycle.

Referring now to FIGS. 8 a through 8 d, they show an example ofpulse-width modulation and its possible affects on the films propertiesfor SiO2 and or SiOxNy. A sign wave signal is used to drive the pulsingfrequency at a fixed peak power level to increase or decrease the shortterm average power into the plasma. The sign wave shown is the drivesignal, and it also indicates power.

At the beginning portion (left side) of the FIG. 8 a, the modulationincreases the power level per given time interval by increasing theon-time and decreasing the off-time of the plasma, thus increasing theinstantaneous radical density and electromagnetic components of theplasma. This process increases the radical density to the point at whichall material was converted and deposited and a new material is thedominate contributor to the growing film stack, SiO2 or SiOxNy. FIG. 8 bshows the dense layer formed next to the substrate during this phase.

In the center of the drive signal, the on-time is at its lowest andoff-time at its highest value. This effect decreases the instantaneousradical density to the point at which all material was consumed and theprecursor material again becomes the dominate contributor to the growingfilm stack. FIG. 8 c shows the less-dense, more-organic layer formedduring the second phase. This layer is deposited on the first layer.

Finally in the last portion of the waveform, the process returns tosaturation of the radical density like in the first portion of thewaveform. This phase deposits a hardened, dense layer. FIG. 8 d showsthe dense, third layer deposited on the second layer. Accordingly, thethree phases together leaving an inter layer of organic material betweentwo hard, dense layers—thereby introducing flexibility into the entirefilm stack.

These modulation techniques can be used during inline or dynamicdeposition processes. By utilizing these modulation techniques with thedynamic deposition process, it is possible to produce alignment layersfor applications such as LCD displays, thereby replacing the polymidelayers presently being used.

In summary, this discovery allows the user to achieve PECVD films notpossible in the past, possibly with extended film properties andqualities not possible to date. The higher quality thin films areachieved from the ability to actively control the plasmasradical/electromagnetic radiation densities in continuous way per unittime by contouring the average and or peak power level per timeinterval. The drive waveform can be any waveform or even an arbitraryfunction. This technique can also be used to control the localizedetching rate when the source and system is configured to do so.

In conclusion, the present invention provides, among other things, asystem and method for controlling deposition onto substrates. Thoseskilled in the art can readily recognize that numerous variations andsubstitutions may be made in the invention, its use and itsconfiguration to achieve substantially the same results as achieved bythe embodiments described herein. Accordingly, there is no intention tolimit the invention to the disclosed exemplary forms. Many variations,modifications and alternative constructions fall within the scope andspirit of the disclosed invention as expressed in the claims.

1. A substrate coated with a thin film, the substrate formed by:generating a first electrical pulse having a first pulse width; usingthe first electrical pulse, generating a first density of radicalizedspecies; disassociating a first portion of a feedstock gas using thefirst density of radicalized species, thereby creating a first pluralityof deposition materials; depositing the first plurality of depositionmaterials on the substrate as a first layer; generating a secondelectrical pulse having a second pulse width, wherein the second pulsewidth is different from the first pulse width; using the secondelectrical pulse, generating a second density of radicalized species;disassociating a second portion of a feedstock gas using the radicalizedspecies in the second density of radicalized species, thereby creating asecond plurality of deposition materials; and depositing the secondplurality of deposition materials on the first layer.
 2. A substratecoated with a thin film, the substrate formed by: generating a plasmahaving a density of radicalized species, wherein the plasma is generatedusing a power signal; disassociating a first portion of a feedstock gasusing the radicalized species in the first density of radicalizedspecies, thereby creating a first deposition material; depositing thefirst deposition material on the substrate, thereby forming a firstlayer; modifying the density of radicalized species by modulating thepower signal used to generate the plasma; disassociating a secondportion of the feedstock gas using the radicalized species in themodified density of radicalized species, thereby creating a seconddeposition material; and depositing the second deposition material onthe first layer, thereby forming a second layer.
 3. The substrate ofclaim 2, further formed by: modifying the density of radicalized speciesby modulating the power signal used to generate the plasma, therebycreating a third density of radicalized species; disassociating a thirdportion of the feedstock gas using the third density of radicalizedspecies, thereby creating a third deposition material; and depositingthe third deposition material on the second layer, thereby forming athird layer.
 4. The substrate of claim 2, wherein the first layer andthe second layer comprise separate layers of deposition material withina film deposited on the substrate.
 5. The substrate of claim 2, whereinthe first layer and the formed second layer comprises a single gradientstack deposited on the substrate.
 6. The substrate of claim 2, whereinmodifying the density of radicalized species by modulating the powersignal used to generate the plasma comprises: modulating an amplitudecharacteristic of the power signal used to generate the plasma.
 7. Thesubstrate of claim 2, wherein modifying the density of radicalizedspecies by modulating the power signal used to generate the plasmacomprises: modulating a frequency characteristic of the power signalused to generate the plasma.
 8. The substrate of claim 2, whereinmodifying the density of radicalized species by modulating the powersignal used to generate the plasma comprises: modulating a pulse widthcharacteristic of the power signal used to generate the plasma.
 9. Thesubstrate of claim 2, wherein modifying the density of radicalizedspecies by modulating the power signal used to generate the plasmacomprises: modulating a pulse position characteristic of the powersignal used to generate the plasma.
 10. The substrate of claim 2,wherein the power signal comprises a high-frequency signal forgenerating the plasma.
 11. The substrate of claim 2, wherein the powersignal is usable by a high-frequency generator so that thehigh-frequency generator can generate a high-frequency signal forgenerating the plasma.
 12. The substrate of claim 11, wherein thehigh-frequency signal comprises microwaves.
 13. A substrate coated witha film, the substrate formed by: generating a first electrical pulsehaving a first pulse amplitude; using the first electrical pulse togenerate a first density of radicalized species; disassociating a firstportion of a feedstock gas using the radicalized species in the firstdensity of radicalized species, thereby creating a first depositionmaterial; depositing the first deposition material on the substrate;generating a second electrical pulse having a second pulse amplitude,wherein the second pulse amplitude is different from the first pulseamplitude; using the second electrical pulse to generate a seconddensity of radicalized species; disassociating a second portion of thefeedstock gas using the radicalized species in the second density ofradicalized species, thereby creating a second deposition material; anddepositing the second plurality of deposition materials on the firstdeposition material.